The purpose of this proposal is to isolate and characterize a novel streptococcal surface receptor that selectively binds the key fibrinolytic component plasmin. The enzymatic activity is protected from inhibition when plasmin is bound to the bacterium. The potential role for bacterial-associated proteolytic activity in the pathogenesis of streptococcal infections will be addressed by the following studies. 1. Purification of functional receptor. 2. Biochemical and immunochemical characterization of the receptor. 3. Assessment of the regulation of receptor bound plasmin. 4. Cloning and sequencing the gene coding for the bacterial plasmin receptor. These investigations will define the relationship of the plasmin receptor to the plasminogen activator, streptokinase.